1. Field of the Invention
The present invention relates to a motor control device for controlling an operation of a motor. The present invention also relates to a motor drive system including this motor control device.
2. Description of Related Art
Conventionally, a motor control device without a rotor position sensor (a position sensor-less motor control device) is developed. This a motor control device estimates a rotor position in a motor without a rotor position sensor and controls the motor base on the estimated rotor position. FIG. 21 shows an example of a block diagram for a motor control device 103 of this type. In the structure shown in FIG. 21, an estimated axis for the control corresponding to a d-axis in a vector control of a motor is a γ-axis, while an estimated axis for the control corresponding to a q-axis is a δ-axis. FIG. 23 shows a relationship among the d-axis, the q-axis, the γ-axis and the δ-axis. The reference numeral Eex in FIG. 23 represents a voltage vector that is usually called an extension induction voltage (an extended electromotive force).
A current detector 11 detects U-phase current iu and V-phase current iv of motor current supplied from a PWM inverter 2 to a motor 1 that is a salient pole machine. A coordinate converter 12 converts the U-phase current iu and the V-phase current iv into γ-axis current iγ and δ-axis current iδ. A position/speed estimator 120 (hereinafter referred to as “estimator 120” simply) estimates and outputs an estimated rotor position θe and an estimated motor speed ωe.
A subtracter 19 subtracts the estimated motor speed ωe given by the estimator 120 from a specified motor speed value ω* and outputs the result. A speed controller 17 generates a specified δ-axis current value iδ* to be followed by the δ-axis current iδ based on the subtraction result (ω*−ωe) from the subtracter 19. A magnetic flux controller 116 outputs a specified γ-axis current value iγ* to be followed by the γ-axis current iγ based on the specified δ-axis current value iδ* and the like. A current controller 15 outputs a specified γ-axis voltage value vγ* and a specified δ-axis voltage value vδ* so that both a current error (iγ*−iγ) and a current error (iδ*−iδ) given by the subtracters 13 and 14 converge to zero.
A coordinate converter 18 performs inverse conversion of the specified γ-axis voltage value vγ* and the specified δ-axis voltage value vδ* based on the estimated rotor position θe given by the estimator 120 and generates specified three-phase voltage values including a specified U-phase voltage value vu*, a specified V-phase voltage value vv* and specified W-phase voltage value vw*, which are supplied to the PWM inverter 2. The PWM inverter 2 generates a signal modulated by pulse width based on the specified three-phase voltage values (vu*, vv* and vw*) and supplies the motor 1 with motor current corresponding to the specified three-phase voltage values for driving the motor 1.
FIG. 22 shows an inside structure of the estimator 120. The estimator 120 includes an axial error estimator 130, a proportional-plus-integral calculator 131 and an integrator 132. The axial error estimator 130 estimates an axial error Δθ between the d-axis and the γ-axis. The axial error estimator 130 calculates the axial error Δθ by using the equation (1) below, for example. Here, Ld and Lq represent a d-axis inductance and a q-axis inductance of the motor 1, respectively, and Ra represents motor resistance of the motor 1. Furthermore, s is the Laplace operator. There are proposed various methods for estimating a rotor position. In many cases, a value of q-axis inductance of a motor is used as an operation parameter in a calculation equation for estimation as the equation (1) below.
                                                                                             Δ                  ⁢                                                                          ⁢                  θ                                =                                                      tan                                          -                      1                                                        ⁡                                      (                                                                  -                                                  E                                                      ex                            ⁢                                                                                                                  ⁢                            γ                                                                                                                      E                                                  ex                          ⁢                                                                                                          ⁢                          δ                                                                                      )                                                                                                                          =                                                      tan                                          -                      1                                                        ⁡                                      (                                                                  -                                                  (                                                                                    v                              γ                              *                                                        -                                                                                          (                                                                                                      R                                    a                                                                    +                                                                                                            L                                      d                                                                        ⁢                                    s                                                                                                  )                                                            ⁢                                                              i                                γ                                                                                      +                                                                                          ω                                e                                                            ⁢                                                              L                                q                                                            ⁢                                                              i                                δ                                                                                                              )                                                                                                                      v                          δ                          *                                                -                                                                              (                                                                                          R                                a                                                            +                                                                                                L                                  d                                                                ⁢                                s                                                                                      )                                                    ⁢                                                      i                            δ                                                                          +                                                                              ω                            e                                                    ⁢                                                      L                            q                                                    ⁢                                                      i                            γ                                                                                                                )                                                                                                            (          1          )                    
The above equation (1) is a calculation equation for calculating the axial error Δθ described in Japanese patent No. 3411878 (hereinafter referred to as a first patent document). Note that a difference between the d-axis and the γ-axis (dc-axis) with reference to the d-axis is defined as Δθ in the first patent document while a difference between the d-axis and the γ-axis (dc-axis) with reference to the γ-axis is defined as Δθ, so the sign (negative or positive) is opposite between the calculation equation of the axial error Δθ in the first patent document and the equation (1). Furthermore, in the equation (1), Eexγ and Eexδ represent a γ-axis component and a δ-axis component of an extension induction voltage (an extended electromotive force) Eex, respectively.
The proportional-plus-integral calculator 131 performs a proportional plus integral control in cooperation with each portion constituting the motor control device 103 for realizing a PLL (Phase Locked Loop), and it calculates the estimated motor speed ωe so that the axial error Δθ calculated by the axial error estimator 130 converges to zero. The integrator 132 integrates the estimated motor speed ωe outputted by the proportional-plus-integral calculator 131 and calculates the estimated rotor position θe. The estimated motor speed ωe outputted by the proportional-plus-integral calculator 131 and the estimated rotor position θe outputted by the integrator 132 are imparted as output values of the estimator 120 to each part of the motor control device 103 that needs the values.
Since the motor control device 103 is structured as described above, the axial error Δθ between the d-axis and the γ-axis converges to zero so that a stable motor control can be realized. Note that if the axial error Δθ is maintained at zero, the d-axis current id follows the specified γ-axis current value iγ* while the q-axis current iq follows the specified δ-axis current value iδ*.
The calculation equation for calculating the d-axis current id for performing a maximum torque control utilizing a reluctance torque is known widely. When a maximum torque control is performed by the motor control device 103 having the structure described above, the magnetic flux controller 116 calculates the specified γ-axis current value iγ* based on the equation (2) below. Here, Φa represents armature flux linkage of the permanent magnet.
                              i          γ          *                =                                            Φ              a                                      2              ⁢                              (                                                      L                    q                                    -                                      L                    d                                                  )                                              -                                                                      Φ                  a                  2                                                  4                  ⁢                                                            (                                                                        L                          q                                                -                                                  L                          d                                                                    )                                        2                                                              +                                                i                  δ                  *                                2                                                                        (        2        )            
In addition, JP-A-2003-309992 (hereinafter referred to as a second patent document) discloses a position sensor-less control method, in which a phase of motor current is adjusted so that a value of motor current becomes a minimum value.
In addition, “Position and Speed Sensorless Control for IPMSM Based on Estimation of Position Error”, Sigeo Morimoto et al, T.IEE Japan, Vol. 122-D, No. 7, 2002, pp. 722-729 (hereinafter referred to as a first non-patent document) discloses a relationship between an error of an operation parameter that is used for estimating a rotor position and a position estimation error (the axial error). In addition, Japanese patent No. 3312472 (hereinafter referred to as a third patent document), JP-A-2003-219682 (hereinafter referred to as a fourth patent document), JP-A-2002-51597 (hereinafter referred to as a fifth patent document) and JP-A-2003-153582 (hereinafter referred to as a sixth patent document) disclose motor control techniques utilizing injection of high frequency voltage or high frequency current. In addition, JP-A-H10-94298 discloses a technique concerning switching between a low speed sensor-less control and a high speed sensor-less control.
In order to realize the maximum torque control by using the above equation (2), it is required as a precondition that the axial error Δθ is maintained at zero. On the other hand, the calculation of the axial error Δθ using the above equation (1) needs a value of the q-axis inductance Lq as an operation parameter (a motor parameter). Therefore, in a conventional method, a real value of the q-axis inductance Lq of the motor 1 is studied for performing the maximum torque control so that the real value of the q-axis inductance Lq is used as it is for obtaining the axial error Δθ (and therefore the estimated rotor position θe).
In addition, in order to perform a high efficiency operation by the maximum torque control or the like utilizing the reluctance torque, it is necessary to supply the motor with the d-axis current id corresponding to the q-axis current iq as understood from the above equation (2). Therefore, the specified γ-axis current value iγ* must be calculated sequentially in order to perform the high efficiency operation.
In addition, the calculation equation for calculating the specified γ-axis current value iγ* for performing the maximum torque control or the like includes a plurality of motor parameters whose true values are not known. Therefore, if there are errors between the motor parameters (the operation parameters) that are used for calculating the specified γ-axis current value iγ* and true motor parameters, a desired motor control cannot be performed. For this reason, it is essential to perform an adjustment for decreasing the errors as much as possible. However, the adjustment for the plurality of motor parameters is not easy, and a lot of time is necessary for the adjustment.
When the maximum torque control is performed in the conventional motor control device as described above, it is the first thing to adjust the parameters for maintaining the axial error Δθ at zero (for estimating the rotor position).
Secondly, it is also required to adjust the parameters that are used in the calculation equation (2) for calculating the specified γ-axis current value iγ*.
Thirdly, it is necessary to perform the calculation of the specified γ-axis current value iγ* sequentially that requires a complicated calculation.
The parameter adjustment for the rotor position estimation and the parameter adjustment for calculating the specified γ-axis current value iγ* are performed independently, so more time for the adjustments is necessary. In addition, the error in the adjustment of the parameter for estimating the rotor position and the error in the adjustment of the parameter for calculating the specified γ-axis current value iγ* are affected by each other so that the adjustments become more difficult. In addition, when the adjustments become difficult, optimization of the parameters also becomes difficult resulting in difficulty in realizing an optimal drive of the motor.
Note that the techniques described in the first patent document, the second patent document and the first non-patent document which are described above cannot solve the problem described above. Furthermore, the second patent document utilizes an approximation of Δθ≈0, so estimation accuracy becomes lower as a value of Δθ increases.